Ensure Increase and decrease in allocation are always positive values

Purpose: It does not make sense to show a negative allocation from a budget as an increase in allocation. A negative increase should always be considered a decrease and A negative decrease should be considered an increase. Currently the only way to remove allocated value from a budget without moving it to another fund is to create a negative increase.

User story statement(s):

As a finance librarian,
I want to be able to add or remove allocation from the budget and have it display as increase or decrease
so that I know how much the budget was adjusted up or down.

Acceptance criteria:
Update API validation to align with UI field validation in UIF-280
Make sure calculation is correct when creating a transaction with "To" field empty